3662 solvent evaporated at reduced pressure. Trimethyl borate, 12.8 ml (11.8 g, 113 mmol), and 2.5 ml of 2.42 M borane in THF (catalyst) were added to the crude organoborane and the mixture was heated to 12Cb130” (bath temperature) for 3 hr. Distillation of the resultant products (10-in. concentric tube column) gave, after a forerun (3.05 g), 10.4 g (7473 of B-methoxyborepane (5), bp 74-78’ (32 mm), in ca. 95 purity. The only contaminant was B-OCH3-9BN (ca. 5 % ) as determined by glpc.’* No B-methoxy-2-methylborinane (10)was detected. Reactivity of 9-BBN (13) and Borepane (2) toward Ring Opening by Borane. (a) 9-BBN. To 32.8 ml (20 mmol) of 0.611 M 9BBN in T H F at ca. 25” was added 1.61 ml (10 mmol) of +octane (glpc standard) followed by 8.3 ml (20 mmol) of 2.40 M borane in THF. At periodic intervals 10-ml samples of the solution were treated with 1.1 ml (28 mmol) of methanol and analyzed by glpc for B-OCH3-9-BBN.I8 After 48 hr only a 0.7-mmol ( 3 . 5 % ) loss of 9-BBN was observed. Infrared spectral analysis after addition of borane revealed bands at 2400 cm-I (s) (BH, in THF), 1550 cm-’ (s) (BH2B bridge), and weak bands in the 25OC-2600 cm-I region (terminal B-H of R3BH.BH3 complex). No change in the spectrum was observed in 48 hr. (b) Borepane (2). A T H F solution of borepane (theory 25 mmol), 9-BBN (theory 50 mmol), and /?-octane (15 mmol) was prepared in the manner previously described for the exchange reaction of 14 at reflux. The final volume of the solution was adjusted
to 110 ml with dry THF. Glpc analysis’8 of a 10-ml methanolyzed sample indicated a 22.2 mmol (89%) yield of borepane and 45.7mmol (91 %) yield of 9-BBN. The remaining reaction mixture was divided into two 50-ml portions. To one was added 4.7 ml (11.3 mmol, equal to theoretical quantity of borepane) and the other 9.4 ml (22.6 mmol, twice the theoretical quantity of borepane) of 2.4 M borane in T H F at ca. 25”. At scheduled intervals 5ml samples were methanolyzed and analyzed by glpc for B-methoxyThe quantity of 5 present after borepane (5) and B-OCH2-9-BBN. 48 hr was 19.1 mmol in the former experiment and 14.2 mmol in the latter experiment. This represents a 14 and 3 6 z loss of borepane, respectively, based on the experimentally determined initial quantity. Small amounts of tetramethyl 1,6-hexanediboronate (15) were observed in the 48-hr glpc analysis in the latter experiment (identified by comparison of retention time with authentic sample). No significant changes in the amount of 9-BBN present were observed in either experiment.
Acknowledgments. The authors gratefully acknowledge the assistance of Dr. R. E. Cook and staff for assistance in obtaining mass spectral data, and the financial support of this research by the U. S . Army Research Office (Durham) and the National Institutes of Health.
Selective Deoxygenation of Ketones and Aldehydes Including Hindered Systems with Sodium Cyanoborohydride’ Robert 0. Hutchins,* Cynthia A. Milewski,2 and Bruce E. Maryanoff
Contribution f r o m the Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104. Received October 16, 1972 Abstract : T h e reduction o f aliphatic ketone and aldehyde tosylhydrazones with sodium cyanoborohydride in acidic 1: 1 DMF-sulfolane provides a mild, convenient, and high-yield method for deoxygenation without the production of side products. Noteworthy features and advantages of the procedure include : (a) superior selectivity in that most other functional groups (i.e., ester, amide, cyano, nitro, chloro) are not affected under the reaction conditions allowing carbonyls t o be removed in their presence; (b) most hindered carbonyls a r e reliably reduced t o hydrocarbons without side reactions ; (c) a$-unsaturated carbonyls are reduced in good yields specifically t o alkenes with migration of the double bond; (d) a limitation of the method involves aryl carbonyls which are resistant t o reduction unless the ring is substituted with an electron donating group.
key functional group transformation which often presents itself in organic synthesis is the converof carbonyl derivatives to methyl or methylene groups after such intermediates have served their synthetic purpose of activating molecules for the host of reactions essential for building complex structures. Consequently, a voluminous amount of literature exists concerning direct or indirect 3 , deoxygenation
A sion
(1) A preliminary account of portions of this work has been previously reported: R. 0. Hutchins, B. E. Maryanoff, and C. A. Milewski, J . Amer. Chem. Soc., 93, 1793 (1971). (2) National Science Foundation undergraduate research participant, 1971. (3) Excellent recent critical reviews of deoxygenation methods are available; see W. Reusch in “Reduction,” R . L. Augustine, Ed., Marcel Dekker, New York, N. Y., 1968, pp 171-21 1 ; (b) H . 0. House, “Modern Synthetic Reactions,” 2nd ed, W. A . Benjamin, Menlo Park, Calif., 1972, Chapter 4. (4) A common and often effective indirect method involves the reduction of carbonyl derivatives to alcohols, which are converted to a suitable leaving group and subsequently displaced by a hydride source, usually lithium aluminum hydride (ref 3a and 3b, Chapter 2; and C. W. Jefford, D. I
